For the last twenty years, I have managed to transform an obsession with PL/SQL into a paying job. How cool is that?

Monday, March 21, 2016

Accessing index of associative array in SELECT-FROM TABLE() operation

As of Oracle Database 12c Release 1, you can now use the TABLE operator with associative arrays whose types are declared in a package specification. Prior to 12.1, this was only possible with schema-level nested table and varray types. Here's a quick example:

And with nested tables and varrays, the index values used in those collections are usually not very interesting. Varrays are always densely-filled (no gaps between first and last index values). Nested tables are (or should be treated as) multisets - the order of its elements is not significant.

But with associative arrays, index values can be negative. They can be strings. And it is not terribly uncommon for associative arrays to be sparse (not every index value defined between first and last).

What if you need to access those index values in the dataset returned by the TABLE operator? In this case, I am sorry to have to tell you, you have to do some extra work. That information simply isn't available natively - which, I think, is quite reasonable. When you use SELECT-FROM TABLE you are saying, in effect, I want to treat the data as a virtual tables. Tables don't have indexes built into them. You have to specify them "on top" of the table.

In any case, the solution isn't terribly difficult. You simply add a field to your record (or attribute to object type). Or if your collection is currently a collection of scalars (list of dates or strings or numbers), then you will have to create a record or object type to hold that scalar value, plus the index value. Then that index value is available as "just another column" in your query.

Here are the steps:

1. Recompile the package specification, after adding an index field. The package body remains the same as above, so I won't repeat it below.